Polymers derived from the ring opening polymerizations of benzoxazine compounds compete with phenolic, epoxy, and other resins in various applications. Benzoxazines have advantages over conventional phenolic resins as the benzoxazine can be readily molded from the melt and then polymerized by simply heating it without releasing reaction by-products.
Phenolic resins have been used for years in applications requiring low flammability and high char yields. These uses include aircraft interiors which often include a thin layer of flame inhibiting phenolics in the interior shell and in electronics such as circuit boards, connectors, etc. A drawback of many phenolics are volatiles which may be produced during crosslinking (said volatiles often producing undesirable voids in the finished article) and residual catalyst and other reactants retained in the resins (which impart undesirable color or undesirable properties on aging. Benzoxazines avoid these problems (volatiles and residuals) due to polymerizing by a method not producing volatiles (supposedly ionic ring opening polymerizations) and not requiring catalysts. Having lower viscosities, the benzoxazines are easier to mold than phenolics.
Another use for benzoxazine polymers is as a precursor for chars produced between 400 and 800.degree. C. In this application they compete with coal tar pitch and phenolic resins which can produce between 30 and 65 weight % char upon exposure to elevated temperatures. These chars are useful as components in aircraft brakes and as thermal insulators or barriers.
As the char yield of polymers from benzoxazines are in the same ranges as coal tar pitch and phenolic resins there has been little motivation (other than processability and properties for non-char forming applications) to use benzoxazines.